Gas sensor arrangements for detecting a wide variety of analytes, for example methane or carbon dioxide, are well known. Examples of such gas sensors are disclosed in EP 0616207 A2, WO 00/55603 A1, and DE 19925196 C2. The gas sensors comprise a radiation source, a gas measuring chamber, and a radiation detector. The gas sensors are based on the principle that a large number of polyatomic gases absorb radiation, particularly in an infrared wavelength range. The absorption occurs in a wavelength characteristic for the gas, for example at 4.24 μm for carbon dioxide. Using gas sensors, it is therefore possible to detect the existence of a gas component and/or the concentration of the gas component. The intensity of the radiation measured by the radiation detector is a measure of the concentration of the gas. Either a broadband radiation source may be used and the wavelength of interest adjusted via an interference filter or grid or a selective radiation source may be used, for example a light-emitting diode or a laser, in combination with non-wavelength-selective radiation receivers.
It is known from EP 0616207 A2 that bundling the radiation emitted from the radiation source increases the energy efficiency of the gas sensor. In order to bundle the emitted radiation, a concave mirror is positioned at a point at which the radiation detector is located and a metal funnel-shaped tube is arranged in front of the radiation detector so that the emitted radiation is focused onto a detection surface of the radiation detector.
In the motor vehicle sector, the detection of carbon dioxide is becoming increasingly important. For example, to increase energy efficiency during heating and air conditioning, the carbon dioxide content of the air in the interior of the vehicle is monitored. In the event that an increase in carbon dioxide concentration occurs, a supply of fresh air is introduced via a fan flap. Additionally, modern air conditioning systems are based on carbon dioxide coolants. The gas sensors can therefore fulfill a monitoring function in conjunction with issuing carbon dioxide in the event of potential defects. Gas sensors of this type, however, must meet stringent requirements with respect to ruggedness, reliability, and miniaturization.